Sean Young at the University of California, Los Angeles, and his colleagues analysed tweets posted in 2012. They narrowed down millions of posts to 8538 tweets that could be geolocated to US counties and included keywords such as “sex” or “suck” used in a sexual context. Areas where sexual tweets were posted saw a 2.7 per cent increase in syphilis rates the following year.

One way to predict an increase in syphilis rates is to look at the current number of cases – for example, each county that had a higher than average number of cases in 2012 saw a 0.6 per cent increase the following year. Tweets corresponded to